Understanding the physiology of children is essential for any sports coach, writes Dr Giles Warrington
WHEN IT comes to their physiology, children are not small adults. During the different phases of growth and development, they differ quite significantly. In young athletes, for example, there are critical physiological and musculoskeletal differences that will have an impact on the effects of training which are quite different to those of adult performers.
Despite this, watered-down adult exercise and training programmes are often imposed on children and teenagers which may be inappropriate to their stage of maturation and may lead to injury, overtraining, burn-out and even a complete withdrawal from physical activity and sport.
As a consequence, training children at any age must take into account the complex and multi-factorial nature of physical activity and sports participation.
There is no doubt that there are many potential benefits from young children being physically active, and opportunities to engage in regular sport and exercise should be provided to as many children as possible irrespective of ability, age, gender or social background.
Debate is ongoing as to the appropriate types of exercise and training that young children and adolescents should engage in. To answer this, it is firstly important to have an elementary understanding of paediatric physiology and the process of growth and maturation which form the central cogs of a child's physical development.
During their critical stages of development, children do not grow at an even rate. The rate of growth is most pronounced immediately after birth and, in fact, an infant will reach approximately 50 per cent of their adult height by two years of age.
From two years onwards, despite small surges, the rate of growth is relatively consistent until the growth spurt associated with puberty which carries them through maturation, where there is a marked growth of up to 15cm over two years.
The start of the growth spurt, signalling the commencement of puberty, is also referred to as the "onset of peak height velocity" initiating a point of rapid growth, which generally begins two years earlier in girls around the age of 10-12 years, with boys maturing later at 12-14 years.
Developmental issues have a key role to play in a child's physical progression and skill acquisition. Within a group of pre-adolescents, the start and rate of maturation is highly variable and the difference between chronological age and biological age may vary by as much as three to four years.
Consequently, from a physiological and musculoskeletal perspective, no two 14 year olds are the same. This growth variability clearly has implications for age-group sports as the early bloomers have a distinct physical advantage over the late developers.
A phenomenon related to this area is what has been referred to by researchers as the "birth date effect", where it has been shown in a variety of activities and sports that the older individuals within a certain age group may have a higher level of skill proficiency and physical prowess, thereby increasing the likelihood of them being picked for the team.
Flexibility refers to the range of motion around a specific joint in the body and is affected by the tension of the muscle and tendons attached across the joint. Current data suggests that the flexibility of children appears to be affected by genetic and movement specific factors.
Generally, children may have very loose, mobile joints referred to as hypermobility which appears to be more common in girls than boys. Although a good range of motion around the key joints is important for normal functionality, hypermobility in children may lead to joint laxity and injury in later years unless the supporting muscles are strengthened.
During maturation, flexibility is generally reduced as the long bones increase in length causing the muscles to be stretched. Unless appropriate stretching programmes designed to maintain and improve flexibility are implemented during adolescence and adulthood, poor flexibility can lead to a decrease in range of motion and may cause an increased risk of overuse type injuries.
The composition of the body is made up predominantly of muscle, fat and bone. As a proportion of overall body composition, the amount of fat that accumulates with growth and ageing depends on genetics, nutrition and exercise habits.
At birth, approximately 10-12 per cent of body mass is fat. At about eight years, girls and boys will have similar body fat levels in the region of about 16-18 per cent. In contrast, in post puberty there is a large divergence with girls increasing their body fat to about 25-27 per cent while boys may typically reduce their levels to about 12-15 per cent. These gender differences have been shown to be predominantly due to hormonal factors associated with maturation.
Strength improves as muscle mass increases with age and peaks at about 20 years of age in females and 20-30 years in males with the rate of strength gain most noticeable around puberty due to hormonal factors.
Despite this, scientific evidence has shown that training can lead to strength improvements even in pre-pubescent children and those as young as six years have been shown to benefit from strength training.
These strength improvements in young children prior to maturation appear to be related to neural and co-ordination factors as well as skill development, rather than increases in muscle mass.
Pre-adolescent children are, by nature, aerobic animals as they do not have a highly developed anaerobic system. As a consequence, prior to maturation the potential to improve aerobic endurance capacity is only limited.
Instead, emphasis should be placed on the enhancement of co-ordination, balance and skill development. Understanding the basic differences in the physiology of children is, therefore, essential for any coach or parent involved in under-age sports and exercise programmes.
Dr Giles Warrington is a sports and exercise physiologist and lecturer in the School of Health and Human Performance at Dublin City University